Kala azar, also known as Visceral Leishmaniasis (VL), is a neglected tropical disease caused by the parasite Leishmania donovani. It is prevalent in South Asia, East Africa, and South America, primarily affecting impoverished and marginalized communities in remote and rural areas with limited healthcare access.
Historically, Kala azar has been recognized in India and other endemic regions for centuries. Early accounts from the 19th century describe symptoms resembling visceral leishmaniasis. However, it was not until 1903 that the causative parasite, Leishmania donovani, was identified by Sir William Leishman, a British bacteriologist working in India. The disease acquired its name "Kala azar" from Hindustani, meaning "black fever," in reference to the grayish discoloration of the patient's skin.
Kala azar is endemic in approximately 65 countries worldwide, with India, Bangladesh, Nepal, Sudan, South Sudan, and Brazil accounting for the majority of cases. These countries represent around 90% of reported global cases. However, there is a potential for outbreak and the disease can affect other regions under specific circumstances.
The primary mode of transmission for Kala azar is through the bite of infected female sand flies belonging to the Phlebotomus genus (such as Phlebotomus argentipes and Phlebotomus orientalis) in the Indian subcontinent and the Lutzomyia genus (such as Lutzomyia longipalpis) in the Americas. These sand flies acquire the parasite by biting an infected human or animal reservoir.
Kala azar affects both children and adults, although children under 15 are most vulnerable to severe forms of the disease. Poverty, malnutrition, and weakened immune systems contribute to increased susceptibility in endemic areas. Additionally, conditions such as HIV/AIDS, tuberculosis, and malaria increase the risk of developing or exacerbating Kala azar.
According to the World Health Organization (WHO), there are an estimated 50,000 to 90,000 new cases of Kala azar globally each year. However, due to underreporting and limited surveillance systems, the actual number of cases is likely higher. The estimated annual death toll ranges from 20,000 to 40,000 people. India alone reportedly accounts for approximately 70% of the global burden of Kala azar.
Several factors contribute to the transmission of Kala azar, including proximity to sand fly breeding sites, poor housing conditions, limited access to effective vector control measures, migration of infected individuals, and inadequate availability and accessibility to diagnosis and treatment services.
The impact of Kala azar varies among regions and populations. Sudan and South Sudan have the highest burden in Africa, accounting for over 50% of global cases. In India, the disease is endemic in the eastern states, particularly Bihar, Jharkhand, and West Bengal. Nepal and Bangladesh also have significant prevalence rates. Brazil is the most affected country in South America. Within these regions, marginalized and vulnerable populations such as migrant workers, refugees, and displaced persons bear a disproportionate burden of the disease.
Prevalence rates of Kala azar can vary within countries and even within different regions of the same country. Factors such as variations in sand fly distribution and behavior, local ecological conditions, and access to healthcare services contribute to these variations. Socioeconomic disparities, including poverty and limited healthcare infrastructure, further amplify the impact of Kala azar on vulnerable populations.
In conclusion, Kala azar is a neglected tropical disease that significantly affects communities in South Asia, East Africa, and South America. Transmission occurs primarily through sand fly bites, and it disproportionately impacts marginalized and vulnerable populations. To reduce the burden of Kala azar globally, improved surveillance, effective vector control measures, increased access to diagnosis and treatment, and enhanced public health interventions are crucial.

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Seasonal Patterns: Kala azar cases in mainland China exhibit a consistent peak from October to December, followed by a decline from January to March. This pattern recurs with variations throughout the years, with the highest number of cases occurring in October and the lowest in January.
Peak and Trough Periods: The peak period for Kala azar cases in mainland China is observed in October, with an average of 45 reported cases. This is followed by a trough period in January, where the average number of cases decreases to 16. These peak and trough periods indicate a seasonal fluctuation in Kala azar cases, with higher transmission during colder months.
Overall Trends: Overall, there is a slight decreasing trend in Kala azar cases in mainland China from 2010 to 2023, except for a sharp increase in 2015. The number of cases ranged from as few as 9 in 2012 to as many as 123 in 2015. After 2015, there is a general decline in cases, with some fluctuations in the number of reported cases over the years.
Discussion: The observed seasonal patterns in Kala azar cases in mainland China suggest a cyclical trend with a peak in the winter months, aligning with the known transmission dynamics of the disease. The lower number of cases during the summer months may be attributed to factors such as vector activity, environmental conditions, or human interventions. The overall decreasing trend in Kala azar cases is promising and may indicate successful control efforts implemented in recent years. However, the occasional sharp increases in certain years, such as 2015, emphasize the necessity for continued surveillance and control measures to prevent outbreaks and sustain the declining trend in cases.